A new study suggests a link between blood sugar and food cravings — but in some obese people, this link may be broken.

According to ABC, scientists showed pictures of high-calorie foods, low-calorie foods, and non-food items to five obese subjects and nine non-obese ones. When the non-obese subjects had low blood sugar, imaging revealed elevated activity in their brains' reward centers, which scientists say corresponds to cravings. But when their blood sugar returned to normal, so did their brain activity. However, the obese participants showed elevated activity in response to high-calorie foods irrespective of their blood sugar. Says study co-author Rajita Sinha,

This is significant for the obesity epidemic, as it shows for the first time that obese individuals may have a particularly hard time restraining themselves when faced with high calorie foods and food cues in the environment, and that they are at greater risk for giving in and consuming high-calorie foods.

Of course, not all obese people overeat, and there's not necessarily a direct link path from elevated reward center activity to cravings to behavior — the study authors don't appear to have asked subjects whether they felt they experienced cravings, or to have examined their actual diets. Still, the study does hint at a complex relationship between metabolism, brain activity, and weight, one that might someday help clinicians treat metabolic disorders.